1. Field of the Invention
The present invention relates to laminated foil strip conductors consisting of a band or bands of metal foil or strip which are laminated onto or between dielectric materials in tape form. The materials are usually combined in a continuous process wherein the dielectrics are laminated onto one or both sides of the conductor or folded around it to fully or partially enclose it in an insulating sheath.
2. Background
Typical uses for foil strip conductors are as safety or grounding shields, or as electrostatic screens placed between the primary and secondary windings in transformers. Another use is as winding conductors replacing magnet wire in electric coils for the purpose of raising the space factor or to improve heat dissipation and/or high frequency performance.
A popular type of foil strip conductor consists of metal foil sandwiched between two layers of e.g. polyester film whereof only one is provided with a layer of pressure sensitive adhesive facing the foil strip. Typically in this type material the film layers are from 0.125" to 0.25" wider than than the conductor, and because the non adhesive film adheres to the margins of the opposite film layer but not to the metal it is comparatively easy to peel the sandwich open in order to attach a lead wire to the foil.
Although this type foil strip conductor has gained wide acceptance for many applications it is often considered a drawback that the conductor does not extend all the way to the edges and that the sandwich will sometimes open up unintentionally during application. In addition, often particles of adhesive present near the edges of the sandwich will stick to taping machines which may seize up unless cleaned regularly.
Another version of foil strip conductor, generally referred to as cuffed, comprises a film tape which is laminated onto one side of the foil and folded around both edges extending an equal amount towards the centerline on the other side of the foil. Normally, in the case of a cuffed conductor, an uncovered area is left in the middle which eliminates the need of peeling or stripping for attachment of a ground wire. The open area, however, increases the risk of shorted turns if the tape is accidentally twisted during application, and for this reason a fully enclosed, yet peelable product is preferred by many users.
The experience outlined in the above has led to the development of a variant which is used for similar purposes, comprising a a sheath of a non adhesive film which is folded around the metal strip and sealed on one side by an externally applied strip of adhesive tape. In this product the metal strip is not attached to the inside of the film envelope which may be cut and removed locally for attachment of lead wires. This construction is generally considered sturdier than the sandwich version described above, but still the sealing tape may rub off during rough handling leading to shorted turns in the coils.